1. Field of the Invention
The present invention generally relates to bridge rectifiers for rectifying the current output of an alternating current generator. More specifically, the present invention relates to a high performance bridge rectifier which utilizes an improved first heat sink, an improved carrier plate second heat sink, an improved connection cover of the rectifier, improved first polarity and second polarity diodes, improved diode layout over the first and the second heat sinks, improved diode contact with the electrical contacts of the rectifier, and said rectifier is especially characterized by an improved B+ stud that more efficiently dissipates heat to properly cool the rectifier while providing current to various electrical loads such as, for example, a motor.
2. Background of the Related Art
Bridge rectifiers are used to rectify current output from alternative current sources, such as an alternating current generator. Bridge rectifiers for motor vehicle alternators are well known in the art and generally include two metal parts used as heat sinks that are electrically insulated from each other. As a result of the current that is transmitted therethrough, the bridge rectifier becomes heated due to the internal power loss on each individual diode. Thus, the bridge rectifier must be properly cooled in order to be able to handle the maximum required current, while still being tolerant to increased temperatures due to internal power losses.
Each of the metal parts or carrier plates includes semiconductor diodes that are arranged to polarize the two metal parts into respective positive and negative direct voltage output terminals. The diodes are then connected to respective phase windings of an output winding of the alternating current generator.
The rectifier diodes are connected to respective carrier plates, and these carrier plates are used as heat sinks for these diodes as well. The rectifier diodes are typically inserted by pressure in receiving bore holes of the carrier plate or heat sink, or are soldered to the carrier plate using appropriate solder alloys. The end wires connected to the rectifier diodes enable the rectifier diodes to be connected to external sources.
The heat sinks are typically constructed in the shape of a circle or crescent and are fastened in the same plane to the alternating current generator.
Various difficulties or problems have occurred using this standard diode rectifier. For example, since the diode rectifier is mounted to an alternating current generator that is used with a motor, there are space limitations within the motor, for example, which limit the size of the diode rectifier. One prior art solution to this problem is constructing or fabricating the carrier plates that are connected to the rectifier diodes into a shape that is more than a half circle approximating the circular shape of the alternating current generator. The carrier plates are constructed as a positive heat sink and a negative heat sink and the two heat sinks are arranged coaxially in separate planes spaced apart by an axial distance from one another. See, for example, U.S. Pat. No. 4,952,829 to Armbruster, et al., incorporated herein by reference.
Another problem experienced with diode rectifiers includes the need to carefully match the diode characteristics in order to avoid imbalance in the amount of current conducted by the individual diodes. If thermal imbalance is experienced, certain diodes will increase current flow that may result in thermal runaway. Thermal runaway involves a diode that is unable to regulate its current flow and temperature. In this situation, the diode conducts increased current and experiences increased temperature until the individual diode is no longer able to sustain the normal working reverse voltage, and the diode is destroyed. Frequently, thermal runaway results in the destruction of an individual diode, and the destroyed diode becomes short-circuited thereby rendering the entire bridge rectifier inoperative.
Another problem which has been encountered in bridge rectifiers is that the bridge rectifiers must not only be able to withstand normal battery charging current, but must also be able to supply current, perhaps as much as ten times the normal charging current. These increased current situations may occur, for example, when the motor vehicle is being started. Bridge rectifiers, as discussed, are typically unable to absorb or conduct these types of excess currents and are also unable to rapidly dissipate the resulting heat. Thus, the heat generated within the bridge rectifier may destroy the individual diodes. In order for bridge rectifiers to handle these types of excessive currents and heat, it becomes necessary to utilize a bridge rectifier, which has higher current handling capability. Due to the space limitations of the alternating current generator, it then becomes very difficult to provide such a bridge rectifier from a feasibility standpoint as well as at an economical cost.
A further attempt at increasing the current capacity and heat dissipating characteristics of the bridge rectifier includes the mounting of semiconductor diode chips onto first and second metallic heat sinks, which are electrically insulated from each other by a thin sheet of electrical insulating material. The diode chips are then covered by a protective insulating coating after connection to the respective heat sink. One of the metallic heat sinks includes a finned area, which is subjected to cooling air when the bridge rectifier is mounted to the generator. This type of bridge rectifier is shown in U.S. Pat. No. 4,606,000 to Steele, et al., and is incorporated herein by reference. The heat sink, with a plurality of fins, includes twelve air passages.
FIGS. 1a-1b are prior art illustrations of a similar bridge rectifier as depicted in Steele et al. In FIG. 1a, combined alternator cover and carrier plate 2 includes carrier plate or heat sink 4 connected to alternator cover 6 (only partially depicted to expose underlying plate 4). Carrier plate 4 includes receiving bore holes 8, which are formed for receiving the diodes. Carrier plate 4 includes alternator-mounting holes 10 for mounting carrier plate 4 to the alternator cover 6 via standard connection means, such as a stud or screw connection. Alternator cover 6 includes three main alternator air passages, which interact with the twelve air passages 14 in carrier plate 4, thereby cooling radiating fins 13. As depicted in FIG. 1b (alternator cover 6 omitted for simplicity), carrier plate 4 is of a rectangular shape (in side view) having the air passages 14 going completely through carrier plate 4.
FIG. 2 is a prior art illustration of the positioning of the bridge rectifier 1 within a standard alternating current generator. As depicted in FIG. 2, the completely assembled bridge rectifier 1, which includes carrier plate and cover 1a, is connected to alternator cover 6 via any standard connection means, such as screws 7. Reference numeral 3 denotes the bottom of carrier plate 4, while reference numeral 5 denotes the top of carrier plate 4. Bridge rectifier 1 is also connected to regulator 9. As mentioned previously, the standard bridge rectifier shown in Steele et al. and FIGS. 1a-1b is well known in the art, and may also be purchased from Wetherill Associates Inc. of Royersford, Pa. as part no. 31-113, including cover part no. 46-1858.
FIGS. 3a-3b illustrate a prior art solution presented by U.S. Pat. No. 5,646,838 to Integral Automotive S.A. of Luxemburg, and invented by 3 of the 4 inventors of the present invention, with a bridge rectifier using a first heat sink 84, an insulator layer 80, a second heat sink 4, with heightened plateau area 18 over the base section area 16, and an improved convection surface area over the base section, using ridges 54 for better cooling. Again shown are receiving bore holes 8, alternator-mounting holes 10, cooling radiating fins 13 and air passages 14.
The prior art relates to a bridge rectifier for an alternating current generator, including a first heat sink, an insulating layer disposed on the first heat sink and a second heat sink disposed on the insulating layer. While there have been, as described above, several attempts to increase the current and heat capacity of the bridge rectifier, none of these prior attempts have been completely satisfactory. That is, none of these prior art attempts have increased the current and heat capacity of the bridge rectifier in an economical manner and to a degree where the rectifier can perform satisfactorily for a long period of time.
As a result of dissatisfaction with existing bridge rectifiers, significant problems have been discovered, which are the root cause of the poor performance characteristics of prior art bridge rectifiers. These problems reside in insufficient usage of the local resources offered by the alternator cover. Such local resources include slip-ring-end resources in the conduction surface area, and the resource of the free vertical dimension, which could be used for increased volume of the rectifier carrier plate for improved electrical and thermal conduction and for enhanced forced convection. All prior art designs use standard diodes, not optimized for the specific thermal transfer of each heat sink of the bridge rectifier.
Other problems are related to unbalanced diode layout of the prior art rectifiers, hence unbalanced thermal load applied on the rectifier creating exceedingly hot areas where the risk of failure is greatly increased, and the resulting defects or failures which arise therefrom. Another drawback of the related art is the failure to identify all heat sources of the bridge rectifier, thus creating the possibility of a thermally unbalanced design and extra thermal stress on the diodes. Prior art designs did not consider all means of heat evacuation, especially from the second (positive) heat sink, only focusing on convection, and disregarding features that could also increase conduction. The second heat sink prior art designs also do not use all the means possible to increase the heat sink capacity to transport and dissipate heat from the diodes through both conduction and convection. Conduction and convection surface area and volume are not optimized.
Thus, it would be desirable to provide a high performance bridge rectifier that overcomes the problems of prior art.
Accordingly, it is a principal object of embodiments of the present invention to provide a high performance bridge rectifier, which is able to increase the current and heat capacity characteristics of the bridge rectifier at an economical cost.
It is another object of embodiments of the present invention to provide an increased current and heat capacity bridge rectifier which includes a first (negative) heat sink with maximized conduction surface area, in direct contact with the alternator top coverxe2x80x94the slip-ring-end, allowing increased heat transfer from the negative diodes and from the second (positive) heat sink, through the electrically insulating, but thermally conductive separator foil.
It is yet another object of embodiments of the present invention to provide an increased current and heat capacity bridge rectifier which includes a first (negative) heat sink with optimal thickness, allowing a lower thermal impedance to the heat transfer from the second (positive) heat sink, through conduction, to the alternator slip-ring-end body, offering at the same time reduced production costs. The thickness of this heat sink has been harmonized with the negative diode design, so that maximum heat conduction is possible.
It is still another object of embodiments of the present invention to provide an increased current and heat capacity bridge rectifier which includes a first (negative) heat sink having a new diode layout, for better balancing heat loads on the rectifier, and a lower maximum working temperature.
It is a further object of embodiments of the present invention to provide an increased current and heat capacity bridge rectifier which includes a second (positive) heat sink or carrier plate, having a base section area, increased in height, thereby increasing the volume of the carrier plate to increase the current and thermal characteristics, also the convection surface area. While it is difficult to increase the surface area of the carrier plate in the radial direction, i.e., in the same plane as the carrier plate, it is nevertheless possible to increase the depth or height of the forced-cooling fin-section in the carrier plate and the base section to be coextensive with the cover of the carrier plate, since this additional space had not been previously utilized.
It is yet a further object of embodiments of the present invention to provide an increased current and heat capacity bridge rectifier which includes a second (positive) heat sink or carrier plate, having maximized base contact surface area for optimized conduction to the thermally conductive foil and the first heat sink.
It is still a further object of embodiments of the present invention to provide an increased current and heat capacity bridge rectifier which includes a second (positive) heat sink or carrier plate, having deep grooves on the top face of the base section, offering considerably increased convection area to further cool the rectifier said heat sink. These grooves connect to the vertical radial slots in the base section and plateau section of the heat sink, thus expanding the area of the second heat sink included in the forced convection process, greatly increasing cooling performance.
It is yet still another object of embodiments of the present invention to provide an increased current and heat capacity bridge rectifier which includes a second (positive) heat sink or carrier plate, having a plateau section area with increased height thus enabling a large surface area used for forced convection and better cooled first heat sink and diodes.
It is yet still a further object of embodiments of the present invention to provide an increased current and heat capacity bridge rectifier which includes a second (positive) heat sink or carrier plate, having optimized diode layout for balanced thermal load distribution over the whole heat sink.
It is still another object of embodiments of the present invention to provide an increased current and heat capacity bridge rectifier which includes a second (positive) heat sink or carrier plate, having cylindrical counter bore slots with dome shaped ceilings to accommodate the negative diodes of the first (positive) heat sink, without impeding on the convection surface area of said heat sink carrier plate base section.
It is still yet another object of embodiments of the present invention to provide an increased current and heat capacity bridge rectifier which includes a connection cover, having a bottom area at a certain small distance with respect to the top face of the carrier plate base section, this bottom face having filleted radial edges on the inside and the outside. These fillets and distance allow the low pressure created by the alternator fan in the vertical radial slots to suck in air over the top of the carrier plate base section, and through the grooves, creating a new area cooled by forced convection in the rectifier.
It is still a further object of embodiments of the present invention to provide a rectifier connection cover, having a heightened cylindrical rim on the top outer edge thus blocking airflow in between the plastic diaphragm separating the rectifier-regulator area from the rest of the alternator case and the rectifier, and increasing the airflow over and through the grooves on the top face of the base section and through the radial slots. As a consequence, the working temperature will be further reduced.
It is yet a further object of embodiments of the present invention to provide a rectifier using specially designed passivated diodes, optimized for each of the heat sinks in terms of electrical and thermal conduction.
It is also an object of embodiments of the present invention to provide a rectifier using a specially designed positive stud, having a knurled cylindrical area which will be pressed into the second heat sink or carrier plate for improved electrical contact and low power dissipation, thus further helping in decreasing the thermal load on said heat sink and rectifier.
It is also another object of embodiments of the present invention to provide a rectifier where alloy soldering has been eliminated almost totally, all electrical contacts outside the diode casings being done by mechanical (press-fit) or ultra-sonic methods.
In brief, one embodiment of the present invention is a bridge rectifier for an alternating current generator having a slip-ring-end, comprising: a first heat sink having a first polarity set of diodes; an insulating layer located on the first heat sink; a second heat sink having a second polarity set of diodes and disposed on the insulating layer; a connection cover mounted on the second heat sink; a capacitor connected to the connection cover and to the second heat sink; and a B+ stud mounted on the second heat sink and going through the alternator slip-ring-end, the first heat sink and the insulating layer. In additional embodiments, the second heat sink comprises: a base section including first and second areas; dome shaped holes into the second heat sink and receiving the first polarity set of diodes therein; diode receiving holes in the base section and receiving the second polarity set of diodes therein; and a plateau section disposed on the first area of the base section.
In yet further embodiments, the connection cover is mounted on the base section and covers the second area of the base section. In other embodiments, the B+ stud includes a knurled area comprising knurled teeth, and wherein the stud is inserted into a corresponding hole in the second heat sink with the knurled teeth penetrating the walls of the hole. In other embodiments, the first heat sink comprises a substantially symmetrical diode layout. Further embodiments exist wherein a negative diode is adjacent to a corresponding hole for the B+ stud. In other embodiments, the second heat sink has a heightened plateau section. Further embodiments exist wherein the second heat sink has a substantially symmetrical diode layout.
In yet further embodiments, the second heat sink further comprises radial air grooves disposed on a top surface of the base section. In other embodiments, the second heat sink further comprises dome shaped holes to accommodate the first polarity set of diodes into the base section of the second heat sink.
In additional embodiments, the connection cover has filleted bottom inner and outer edges. Other embodiments exist wherein the connection cover has a heightened radial rim over the outer edge of the top face of the connection cover to block airflow over the top face.
In yet further embodiments, the diodes of the first polarity set of diodes mounted on the first heat sink are of different dimensions than the diodes of the second polarity set of diodes. In additional embodiments, the diodes comprise diode casings, and wherein all electrical contacts which are external to the diode casings are exclusively mechanically press-fit. Alternatively, the diodes may comprise diode casings wherein all electrical contacts which are external to the diode casings are exclusively ultrasonically joined technologies.
In brief, another embodiment of an aspect of the present invention is a heat sink for a bridge rectifier comprising: a plurality of diodes arranged in a substantially symmetrical diode layout; and wherein at least one diode is a negative diode adjacent to a corresponding hole for a B+ stud.
In further embodiments, the heat sink further comprising a heightened plateau section area. The heat sink may also further comprise radial air grooves disposed on the top surface of a base section of the heat sink to maximize convection surface area and allow for radial airflow on the surface. Other embodiments of the heat sink exist further comprising dome-shaped holes to accommodate a first polarity set of diodes into a base section of the heat sink, without impeding on the grooved convection area.
In brief, another embodiment of an aspect of the present invention is a connection cover for a bridge rectifier comprising: a top face; filleted bottom inner and outer edges to facilitate and create airflow over a top surface of a base section of a heat sink; and a heightened radial rim over the outer edge of the top face of the connection cover, to block airflow over the top face, thus facilitating cooling airflow between the connection cover and the top face of the base section of the second heat sink.
In brief, another embodiment of an aspect of the present invention is a B+ stud for a bridge rectifier comprising: a knurled area comprising knurled teeth adapted for insertion into a corresponding hole in a heat sink; wherein the knurled teeth penetrate the walls of the hole.
In brief, another embodiment of an aspect of the present invention is a method to increase the current generating capabilities of a current generating source having a slip-ring-end seating area, comprising the steps of: maximizing conduction area of a first heat sink in contact with the slip-ring-end seating area; decreasing the thickness of the first heat sink; optimizing diode layout on the first heat sink for balanced thermal load on the bridge rectifier; maximizing the conduction area of a second heat sink in contact through an insulating layer of the first heat sink to the first heat sink; heightening a base section of the second heat sink to enhance thermal and electrical conduction through the heat sink; heightening a plateau section area of the second heat sink to enhance forced convection performance of the second heat sink; optimizing the diode layout on the second heat sink for balanced thermal load and heat distribution over the second heat sink; adding radial air grooves on the second heat sink, disposed on the base section top surface to maximize convection surface area and allow for radial airflow on the surface; adding dome-shaped holes on the second heat sink to accommodate a first polarity set of diodes into the base section of the second heat sink; adding filleted bottom inner and outer edges on a connection cover to facilitate and create airflow over the top surface of the base section of the second heat sink; adding a heightened radial rim over the outer edge of the top face of the connection cover to block airflow over the top face; and providing a B+ stud that includes a knurled area comprising knurled teeth, wherein the stud is inserted into a corresponding hole on the second heat sink with the knurled teeth penetrating the hole-walls in the second heat sink body; wherein the first polarity set of diodes, mounted on the first heat sink, are designed for maximum direct bottom thermal conduction to the alternator slip-ring-end, while still retaining intact lateral conduction properties; and wherein a second polarity set of diodes, mounted on the second heat sink, are designed for maximum lateral thermal conduction to the second heat sink, while still retaining intact bottom conduction properties.
Another embodiment of that aspect of the invention exists further comprising contacting all electrical contacts which are external to the diodes exclusively through a mechanical press-fit. Alternatively, all electrical contacts which are external to the diodes are contacted exclusively through ultrasonic technologies.